7 facts on nightmare that you had no idea about

1. Nightmares are a mix of memories and other random information played out in a super disturbing way.

Ever had a terrifying dream that you were kidnapped by random coworkers? Stuck on top of the Leaning Tower of Pisa? The images in nightmares are a mix of memories, recent information you were exposed to, and visual representations of your emotions, Michael Breus, Ph.D., clinical psychologist and fellow of the American Academy of Sleep Medicine, tells BuzzFeed Life. And the plot is usually influenced by your fears and stressors, like being chased or tormented. Nightmares tend to be longer than dreams, with frighteningly realistic and memorable details.

What might be a nightmare for you could be a normal dream for someone else. As long as it creates a strong negative emotional response, it’s a nightmare, says Breus. For example, just dreaming about your horrible ex could be a nightmare for you if it stirs up sadness and anger — even if they’re just sitting on your couch, harmless.

3. It’s true that you can only dream about people you’ve met or seen before… kind of.

When you sleep, your memories are being processed from the short term to long term, says Breus, and these make up most of the images in your nightmares. You can also dream of stuff you’ve seen in movies or books. There can technically be new “characters” in a nightmare, but they’re really an amalgamation of faces you’ve already seen, says Breus.

4. The emotional response to nightmares can actually wake you up.

You know when you wake up frantically at 4 a.m. suddenly realizing you’re not in a zombie apocalypse? Here’s why: Research has shown that a lot of dreaming occurs in the visual cortex, Breus says, which is linked to the amygdala, an emotional response center. During a nightmare, both these get fired up and trigger autonomic arousal of the body. “Your heart starts beating faster, breathing becomes labored, and you can start sweating profusely from a nightmare,” he says. Cue waking up in a panic.

5. Nightmares can’t actually kill you.

“There’s no evidence that a nightmare can physically harm or kill you,” says Breus. However, there is data to show that in people with a weak heart or existing heart condition, increased heart rate during sleep could lead to angina (chest pain due to restricted blood flow to the heart) or possibly heart attacks. As we mentioned before, it’s possible that nightmares could cause increased heart rate, but so could a lot of things, says Breus. So that wouldn’t really be a nightmare doing harm so much as an underlying heart problem.

6. Sometimes, nightmares can be good.

“Some patients I see would be upset if their nightmares stopped,” Pagel says. If they don’t cause significant distress, nightmares can be exciting, and even a major source of inspiration. “People who experience vivid and frequent nightmares tend to be more creative individuals with ‘loose borders,’ meaning they are more imaginative,” Pagel says. In addition to helping process emotions, nightmares can also give pretty useful alternative perspectives on certain issues or people.

7. Some people are at a higher risk for nightmares than others.

Depression, anxiety, and other psychiatric disorders are major risk factors for nightmares, says Breus. Sleep disorders such as insomnia or sleep apnea, are also associated with frequent nightmares. And since many sleep disorders are genetic, it’s possible that chronic and severe nightmares could run in your family.